In general, phenomena such as wrinkles, sags, spots and skin roughness which are caused by aging, UV rays and dryness are well known as factors for damaging the beauty of the skin.
A normal skin looks flat at a glance, but a skin surface has a pattern constituted of fine grooves (sulci cutis) and parts (cristae cutis) surrounded by them, that is, a “texture”. The texture is also given as an important factor taking part in the beauty of the skin, and disturbance and a coarseness change in the texture are a large factor for damaging the beauty of the skin.
To observe the role of the texture from a dermatological point of view, sulci cutis provide a corneum having low flexibility with capability to meet dynamic deformation, and they are a passage for sebum and sweat. Accordingly, the skin can maintain smoothness, gloss and flexibility by spreading a lot of the sulci cutis [J. Soc. Cosmet. Chem. Japan, 27 (3), 1993 and The Nishinihon J. of Derm. 63 (2), 103, 2001].
Further, it is known that observing from an optical point of view, conditioned fine texture raises a reflectance on a skin surface and allows the skin to look white (21st, IFSCC Seminar Lecture Abstract, 124, 2001). Not only the texture is coarsened by dryness, but also the beauty of the skin, that is, the smoothness, the gloss, the flexibility and the whiteness of the skin are lost as the age passes, and the skin is notably coarsened and chapped. Further, a relation between the young and beautiful skin and the well-conditioned texture is often pointed out (for example, Japanese Patent Application Laid-Open No. 170028/2001).
Further, skin diseases such as pustulosis, acne, eczema, psoriasis, lichen, ichthyosis, keratosis and atopic dermatitis bring about a serious change in the appearance and the function of the skin.
A lot of medicines and cosmetics which improve the above matters have so far been known. Vitamins A, C, D and derivatives thereof and urea are widely known as the above medicines. Also, used are substances having an epithelium-abrasive action such as α-hydroxy acids including lactic acid and glycolic acid and β-hydroxy acids represented by salicylic acid. Further, carbohydrate derivatives shown in, for example, Japanese translation of PCT international publication for patent application No. 501940/1999) are known as a medicine provided with an epithelium-abrasive action by inhibiting a corneum binding action. On the other hand, amino acids, polyhydric alcohols, polysaccharides, lipids such as ceramides and various ingredients extracted from natural products are blended with skin external preparations as a conventional skin roughness-improving agent for the purpose of providing a moisture holding effect. Further, ellagic acid, kojic acid, arbutin, hydroquinone and various ingredients extracted from natural products have been compounded with conventional whitening agents.
However, medicines and cosmetic compositions blended with the conventional drug efficacy components described above do not still have satisfactory effects on a change in the skin, and the existing situation is that medicines having excellent effects are desired to be developed.
On the other hand, it is known that retinoids including retinoic acid have various and strong physiologic action such as controlling of proliferation and differentiation of cells and controlling of gene expression. It is reported by researches which have so far been made that retinoids have excellent effects for preventing or treating symptoms or diseases related to dermatopathy caused by dryness, UV rays and aging such as wrinkles, sags and pigmentation of the skin and skin diseases such as psoriasis, lichen, ichthyosis, keratosis, Darier's disease, pustulosis, acne, eczema and atopic dermatitis.
However, because of side effects such as strong irritation and teratogenicity and inferior solubility in water, retinoids have so far been extremely limited in application to cosmetics and medicines.
In light of the conventional problems and existing situation described above, the present invention intends to solve them, and an object thereof is to provide an external preparation composition for preventing or treating symptoms or diseases related to dermatopathy caused by dryness, UV rays, active oxygen and aging such as wrinkles and sags of the skin, pigmentation of the skin, skin roughness and coarse texture, dyskeratosis such as psoriasis, lichen, ichthyosis and Darier's disease and skin diseases such as pustulosis, acne, eczema and atopic dermatitis.
Another object of the present invention is to provide an external preparation composition which is useful as at least one of a wrinkle-improving agent, a coarse texture-improving agent, a skin roughness-improving agent, a whitening agent and a acne-improving agent.